SAN FRANCISCO — The holy grail of retail in the 21st century is to recognize shoppers as they walk into stores — like Amazon.com, the e-commerce giant, does when people visit its website.

David Marcus, president of PayPal, the online payment division of eBay, thinks he has the answer in Beacon, a new gadget the company unveiled on Monday at the TechCrunch Disrupt conference in San Francisco.

Beacon is a three-inch high stick that plugs into an electric wall socket and lets stores automatically identify and authenticate PayPal users as they walk in.

The gadget connects to stores' point-of-sale systems and shoppers' smartphones using a technology called Bluetooth Low Energy, letting consumers pay without launching an application or checking in — actions that are currently needed to pay with the PayPal app. Beacon also does not need GPS, or a cellular phone signal, to work.

This is the latest effort by PayPal to get consumers paying in physical stores with their phones rather than by swiping a credit or debit card. This has proved tough so far because swiping a card is so easy and quick.

"This is the one thing I'm most excited to launch since joining PayPal," said Marcus, who took over the online payment giant in the spring of 2012. "This is the first thing I think that is better than swiping a credit card."

PayPal is opening Beacon to third-party developers on Monday and hopes to encourage the creation of shopping apps that work with the new device in stores.

In the fourth quarter, PayPal plans to pilot the device with some large brands, followed by a "massive roll-out" in 2014, Marcus said.

Beacon will cost less than $100, although PayPal has not finalized the pricing, he noted.

PayPal designed the gadget itself. The project was code-named Blueberry, a reference to the new Bluetooth Low Energy technology and one of the engineers who led the project - Hasty Granbery, who joined PayPal through its 2011 acquisition of start-up Fig Card.